Variable oscillator for code practice (CB7317E)

This circuit is from Popular Electronics from the 90s. The integrated circuit is not very common nowadays.

Battery Current Monitor (CB5254E)
This circuit was found in a 2005 Linear Technology manual. The circuit monitors 12 V batteries in...
Electronic Handler (CB7312S)
This circuit was found in the magazine of radio amateurs 73 in a 90's edition. The components are...
Proximity sensor (CB9570E)
This circuit was found in documentation from the 1980s. The circuit uses several components of the...